Two men have been arrested on suspicion of perverting the course of justice after police launched a probe to find out if lab workers at the health company had doctored the results of blood, urine and hair tests.

The men, who are understood to analysts at the firm, have been questioned over alleged tampering at a lab which is used by more than half of the UK’s police forces.

Bosses at Randox Testing Services - which provides forensic services Cleveland Police - believe there are as many as 484 suspected cases of manipulation at its Manchester office.

A Cleveland Police spokeswoman is reported as saying: “We are working closely with our Crown Prosecution Service (CPS) colleagues to investigate which cases may be affected by the quality issue at Randox.

“We are looking at 28 cases. However the number may reduce as we delve deeper into the individual circumstances.

“The circumstances of the quality failure are being investigated and a criminal inquiry has been launched by Greater Manchester Police.”

Dozens of court cases will now need to be reviewed by the Crown Prosecution Service to see if they were affected by “compromised data”.

A CPS spokesperson said: “We are working with the Home Office, police and the Office of the Forensic Science Regulator to assess the impact of the testing failure at Randox Testing Services.

“This includes establishing which cases have been affected by this issue and working with other agencies to decide what action should be taken in relation to those cases.”

Police forces nationwide have been provided with a list cases that may have been effected.

The Gazette understands that if evidence is found to be false, convictions could be quashed and a flood of compensation claims could follow.

Chf Con Debbie Simpson, of the National Police Chiefs Council, said: “We have been made aware of a quality failure with Randox Testing Services which is currently being investigated and a criminal inquiry has been launched by Greater Manchester Police.

“Randox has provided each force with a list of cases that could have been effected. Working in partnership with the Crown Prosecution Service, we have provided guidance to forces so they are able to review each case to determine if compromised data played a part in prosecution and the CPS will then take appropriate action in any cases identified.

“While this investigation is ongoing, we are working with a number of forensic service providers and the Forensic Science Regulator to ensure that any requirement for forensic services is dealt with in the normal timeframes.”